Method of reducing power provided by a wind power installation based on network conditions

ABSTRACT

A wind park system is disclosed. Briefly described, one embodiment comprises at least one wind power installation having a generator for the delivery of electrical power to an electrical network, characterized in that the power delivered to the network by the wind park is regulated or adjusted in dependence on the network frequency of the electrical network.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/489,186, filed Jul 18, 2006, now U.S. Pat. No. 7,830,029; which is adivisional of U.S. patent application Ser. No. 11/345,034, filed Feb 1,2006, now U.S. Pat No. 7,392,114; which is a continuation of U.S. patentapplication Ser. No. 10/490,896, filed Oct 22, 2004, now U.S. Pat. No.7,638,893; which is a national phase under 35 U.S.C. §371 ofPCT/EP02/10627, filed Sep 21, 2002; which is based on German PatentApplication No. 10148225.6, filed Sep 28, 2001; which applications areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a method of operating a wind park and also a windpark as such.

2. Description of the Related Art

Wind power installations were initially always erected in the form ofindividual units and it is only in recent years that, caused also byadministrative and building regulations, wind power installations arefrequently installed in wind parks. In that respect a wind park in itssmallest unit is an arrangement of at least two wind powerinstallations, but frequently markedly more. By way of example mentionmay be made of the wind park at Holtriem (East Frisia) where more than50 wind power installations are set up in an array. It is to be expectedthat the number of units and also the installed power of the wind powerinstallations will also increase greatly in the forthcoming years. Inmost cases the wind potential is at its greatest in regions of the powersupply networks with a low level of short-circuit power and lowpopulation density. It is precisely there that the technical connectionlimits are quickly reached by the wind power installations, with theresult that it is then no longer possible for further wind powerinstallations to be set up at such sites.

A conventional wind park which is connected, by way of example, to a 50MW transformer substation can therefore provide, at a maximum, only 50MW total power, that is to say, for example 50, wind power installationseach providing 1 MW nominal power.

Bearing in mind that wind power installations are not constantlyoperated in the nominal mode and thus the overall wind park also doesnot constantly reach its maximum power, referred to herein as thenominal power, it can be found that the wind park is not put to optimumuse if the nominal power of the wind park corresponds to the maximumpossible total power which can be fed into the electric grid connectedto the wind park.

Another issue is that in the case of low-power electrical networks, someof which are called island networks, the network frequency rises veryquickly and abruptly if a relatively large consumer is separated fromthe electrical network. The drive machines such as, for example, dieselengines, water wheels and the like require some time in order then toreduce their mechanical and electrical power. During that period of timethose generators produce more energy than is taken from the electricalnetwork. That energy is then consumed for accelerating the generators.That means that the rotary speed and thus also the network frequencyrises.

As many electrical devices, for example, computers, electric motors andthe like, which are connected to the electrical network, are however notdesigned for fluctuating network frequencies or abrupt changes therein,that can result in damage to electrical machines, even going as far asdestruction thereof.

BRIEF SUMMARY OF THE INVENTION

The invention accordingly proposes a solution in which the wind park hasa total power output capacity which is higher than the maximum possiblenetwork feed-in power. When applied to the prior indicated example, thepower output capacity can be raised to a value of over 50 MW, forexample, 53 MW. As soon as the wind speeds are sufficiently high toproduce at the maximum permitted power of 50 MW, the wind parkregulating system according to the invention comes into play andregulates individual or all installations down so that the overallmaximum power output is not exceeded and in such a way that it is alwaysobserved. This means that, at wind speeds above the nominal wind (windspeed at which a wind power installation reaches its nominal power), atleast one or all installations are operated with a slightly throttledpower output (for example, at a power level of 940 kW instead of 1 MW).It also means that at wind speeds less than the nominal amount, the windpower installations are not throttled and the wind park can moreconsistently produce the maximum permitted power in this example 50 MW.

The advantages of the invention are apparent. Overall the networkcomponents of the feed network (network components are, for example, thetransformer and the lines) can be put to optimum use or can have theirloads balanced in the optimum fashion. Utilization of the componentthereof up to the thermal limit is also a possibility. In that wayexisting wind park areas can be better utilized, by virtue of setting upa maximum possible number of wind power installations. The number isthen no longer so severely limited by the existing network capacity.

For controlling/regulating a wind power installation it is desirable ifit has a data input, by which the electrical power output can be set ina range of between 0 and 100% with respect to the nominal power. If, forexample, a reference value of 350 kW is applied to that data input, thenthe maximum power output of that wind power installation will not exceedthe reference value of 350 kW. Any value from 0 to the nominal power(for example, from 0 to 1 MW) is possible as a reference value.

That data input can be used directly for power limitation purposes.

It is however also possible by means of a regulator to regulate thegenerator power output in dependence on the network voltage. The networkvoltage can be based on the wind park network or in the feed-in network.

A further important function will be discussed hereinafter on the basisof wind park regulation. It will be assumed, for example, that a windpark comprises 10 wind power installations which each have a nominalpower output of 600 kW. By virtue of the capacitances of the networkcomponents; also called line capacitances or the limited capacitances inthe transformer substation it will further be assumed that the maximumpower that can be delivered to the network is limited to 5200 kW, alsocalled the “limit power.”

There is now the possibility of limiting each of the wind powerinstallations to a maximum power of 520 kW by means of the referencevalue applied to the data input. Doing this achieves the requirement forlimiting the power to be delivered is always met.

Another possibility involves not allowing the maximum power permitted of5200 kW as the sum of all installations to be exceeded, but at the sametime producing a maximum amount of energy (kW-hours (work)).

In that respect it should be recognized that, at low to moderate windspeeds within the wind park, it frequently happens that the wind powerinstallations at the advantageous sites, these usually are the siteswhich the wind first encounters within the wind park receive a greatdeal of wind. If now all wind power installations are simultaneouslycontrolled down to their throttled value, for example, all to 520 kW,that produced power is admittedly attained by some wind powerinstallations arranged at good sites, while some other wind powerinstallations which however are in the ‘wind shadow’ of the well-locatedwind power installations in the second and third rows have less wind andas a result operate, for example, only at 460 kW power and do not reachthe value of the maximum throttled power of 520 kW. The overall poweroutput from the wind park is accordingly therefore substantially belowthe allowed limit power output of 5200 kW.

The wind park power regulation according to the invention in that caseregulates the individual installations in such a way that the maximumpossible energy yield is set. This means in specific terms that, forexample, the installations in the first row or other good sites areregulated to a higher power (for example, to the nominal power sotherefore no throttling action is carried out. Therefore the overallelectrical power in the wind park rises. Park regulation howeverregulates each individual installation in such a way that the maximumallowed electrical connection power is not exceeded while at the sametime the work produced from the total overall wind park (kWh) reaches amaximum value.

Wind park management in accordance with the invention can be easilyadapted to the respective situations which arise. Thus, for example, itis very simple to effect different throttling with respect to the powerof individual installations if an individual one or a plurality ofinstallations of a wind park are, or have to be taken from the network.If for maintenance reasons, or other reasons, an individual installationor a plurality of installations have to be temporarily stopped.

For controlling/regulating the wind park or the individual installationsit is possible to use a data/control processing apparatus which isconnected to the data inputs of the installations and which, from thewind speed data which are ascertained by each installation, ascertainsthe respective most advantageous power throttling value for anindividual installation or for the entire wind park.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a wind power installation which wouldmake use of the present invention.

FIG. 2 is a graphic of a multi-phase alternating current that can besupplied from the wind power installation of FIG. 1 to the power supplynetwork 6, which illustrates the power factor which may be present onthe line according to principles of the present invention.

FIG. 3 is a block diagram of the control circuit for wind powerinstallation according to principles of the present invention.

FIG. 4 is a view showing the principle of operation of an entire windpark according to the concepts of the present invention.

FIG. 5 shows a frequency/power time graph of a wind power installation.

FIG. 6 shows a block circuit diagram of an inverter of a wind powerinstallation, the inverter being controlled with a microprocessoraccording to the present invention.

FIG. 7 is a view illustrating the coupling of a wind power installationto an electrical network according to the invention.

FIG. 8 is an alternative view in relation to FIG. 7.

FIG. 9 is a view illustrating the coupling of a wind power installationto an electrical network according to one aspect of the presentinvention.

FIG. 10 shows a regulating device according to the invention for theoperation of a wind power installation.

FIG. 11 shows some components of the regulating device 10 as shown inFIG. 10.

FIG. 12 is a view showing the relationship between network voltage andphase angle.

FIG. 13 shows a simplified view of regulation of a plurality of windpower installations, the regulation being separate or common accordingto the respective network situation.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a wind power installation 2 having rotor blades 1 coupledto a rotor shaft that drives a generator 12.

FIG. 2 shows changes that can be made to the power factor to adjust thetotal power delivered to the network.

FIG. 3 is a block circuit diagram showing the control system 10 of awind power installation. It includes a microprocessor μP 20 connected toan inverter apparatus 18 (PWR), by means of which multi-phasealternating current can be fed into the power supply network 6. Themicroprocessor has a power input P, an input for inputting a powerfactor, cos phi (cos ø) and an input for inputting the power gradient(dP/dt).

The inverter apparatus comprising a rectifier 16, a rectifierintermediate circuit and an inverter 18 is connected to the generator ofa wind power installation and receives therefrom the energy produced bythe generator 12, in rotary speed-variable fashion, that is to say, independence on the rotary speed of the rotor of the wind powerinstallation.

The design illustrated in the FIGS. 1-3 serve to illustrate how thepower delivered by a wind power installation can be limited in itsamount to a maximum possible network feed-in value.

FIG. 4 is a view showing the principle of a wind park comprising, forexample, three wind power installations 2 a, 2 b, and 2 c of which—asviewed from the direction of the wind—two are disposed in side-by-siderelationship and the third is positioned behind the first two. As eachof the individual wind power installations has a power input for settingthe power of the respective installation (FIG. 1), the power levels ofan individual wind power installation can be set to a desired value bymeans of a data processing apparatus 11, by means of which the entirewind park is controlled. In FIG. 4 the advantageous sites for the windpower installations are those which the wind first encounters, that isto say the installations 2 a and 2 b.

The present invention also concerns a method of operating a wind parkhaving at least one wind power installation with an electrical generatordrivable by a rotor for delivering electrical power to an electricalnetwork to which the wind power installation is connected. The inventionfurther concerns a wind power installation comprising a rotor and anelectrical generator coupled to the rotor for delivering electricalpower to an electrical consumer, in particular an electrical network.

One object of another aspect of the present invention is to eliminatethe above-described problems when wind power installations or a windpark is connected to the electrical network.

According to this other aspect of the invention, that object is attainedby a method having the features set forth in the claims and a wind powerinstallation having the feature set forth in the claims. Advantageousdevelopments are correspondingly described in the appendant claims.

It is proposed in accordance with the invention, if wind powerinstallations are operated on such low-power networks, that theirmechanical and electrical power is to be controlled in dependence on therising network frequency. That is intended to prevent a further increasein the network frequency or to provide for a reduction in the networkfrequency.

That aspect of the invention is described in greater detail hereinafterby means of an embodiment.

FIG. 5 shows the demand on a wind power installation of a wind park toreduce its output power P in dependence on the electrical frequency f ofthe network. In this case the value of 100% represents the reference ortarget frequency (50 Hz, 60 Hz) of the electrical network. The values100.6% and 102% respectively are correspondingly higher values of thenetwork frequency f.

The electrical power of the wind power installation of the wind park isnot yet reduced, for example, when there is a rise in the networkfrequency by 0.6% (that is to say to 100.6%). If thereafter the networkfrequency rises still further, then the electrical power of the windpower installation is reduced. In the illustrated example the electricalpower of the wind power installation is reduced to zero power when thereis a rise in the network frequency to 102%.

FIG. 6 shows an embodiment of a wind power installation system whichsatisfies that requirement. The wind power installation 2 has adjustablerotor blades 1 whose power output can be changed by use of pitchregulation of the rotor blades so that the electrical power output ofthe wind power installation 2 can be reduced. If, for example, the angleof incidence of the rotor blades 1 relative to the wind is adjusted, theforce on the rotor blades 1 can also be reduced to a desired value andhence the electrical power output reduced. This can be done very quicklyby small, but rapid rotation of the rotor blade to vary its pitch withrespect to the wind. The electrical alternating current from thegenerator 12 which is connected to the rotor which carries the rotorblades 1 is rectified by means of a rectifier 7 and smoothed by means ofa capacitor C. The inverter 4 then converts the dc voltage into analternating current which is delivered to the network L₁, L₂, L₃. Thefrequency of that output current is predetermined by the network. Theregulating apparatus comprising a microprocessor 20 measures the networkfrequency and controls the power switches of the inverter in such a waythat the output frequency corresponds to the network voltage and networkfrequency. If—as described above—the network frequency rises, theelectrical power is reduced, as shown in FIG. 5.

FIG. 7 shows the coupling of a wind power installation 2 to anelectrical network 6, wherein the electrical power produced by the windpower installation is delivered at the network feed-in point 21 into thenetwork via control system 10. A plurality of consumers 8, in theillustrated example diagrammatically shown in the form of houses, areconnected to the electrical network 6.

FIG. 8 shows the regulating apparatus according to the invention. Thediagrammatically illustrated rotor 1 of the wind power installation iscoupled to a generator 12, G, which provides an electrical power whichis dependent on the wind speed and thus the wind power. The ac voltageproduced by the generator 12, G, is firstly rectified by means of theinverter and then converted into an ac voltage which is of a frequencycorresponding to the network frequency. The network voltage at thenetwork feed-in point of the network is ascertained by means of thenetwork frequency detector. As soon as the network frequency exceeds apredetermined value—see FIG. 5—, the electrical power output is reducedin order to counteract a further increase in the network frequency.Accordingly, by means of the regulating apparatus, the network frequencyof the network is regulated to a desired network frequency value, or atleast a further rise therein is prevented.

Regulating the feed in that way of the power delivered by the wind powerinstallation makes it possible to avoid or considerably reduce networkfrequency fluctuations.

FIG. 11 shows some of the main components of the control-regulatingapparatus. The control and regulating arrangement has a rectifier 16, inwhich the ac voltage produced in the generator is rectified. A frequencyconverter 18 connected to the rectifier converts the dc voltage which isinitially rectified in the intermediate circuit, into an ac voltagewhich is fed into the network in the form of a three-phase ac voltage byway of the lines L₁, L₂, and L₃. The frequency converter is controlledby means of the microcomputer 20 which is part of the overall regulatingapparatus. For that purpose the microprocessor is coupled to thefrequency converter 18. The input parameters for regulation of thevoltage, with which the electrical power made available by the windpower installation 2 is fed into the network, are the currentlyprevailing network voltage, the network frequency f, the electricalpower P of the generator, the reactive power factor cos ø as well as thepower gradient dP/dt. As explained later herein, the overall powerprovided by the wind power installation can be quickly changed byadjusting the power factor phase angle cos ø and the power gradientunder control of the microprocessor. The microprocessor 20 embodies theregulation according to the invention in respect of the voltage to befed in, at its desired network frequency.

The present invention further concerns a method of operating a wind parkcomprising at least one wind power installation having an electricalgenerator drivable by a rotor for delivering electrical power to anelectrical network and in particular to the connected consumers thereof.

The present invention also concerns a wind power installation (windpark), in particular for carrying out such a method, comprising a rotorand an electrical generator coupled to the rotor for deliveringelectrical power to an electrical network, and a wind park having atleast two wind power installations.

In the known wind power installations for producing electrical energyfrom wind energy, the generator is operated in parallel mode with anelectrical consumer, frequently an electrical network. During operationof the wind power installation the electrical active power produced bythe generator can vary in dependence on the currently prevailing windspeed. The consequence of this is that the network voltage (magnitudeand/or phase) can also be variable, for example, at the feed-in point,in dependence on the currently prevailing wind speed. The same alsoapplies for the current to be fed in.

In a situation involving feeding the electrical power produced into anelectrical network, for example, a public power network fluctuations inthe network voltage can occur. However, such fluctuations arepermissible only within very close limits, in the interests of reliableoperation of connected consumers.

Relatively large deviations from the reference value in respect of thenetwork voltage in the power supply network, in particular at themedium-voltage level, can be compensated, for example, by actuatingswitching devices such as step transformers, insofar as they areactuated when the values exceed or fall below predetermined limitvalues. In that way the network voltage is kept substantially constantwithin predetermined tolerance limits.

One further object of another aspect of the present invention is toprovide a method of operating a wind power installation as well as awind power installation or wind park, which, even with a fluctuatingactive power delivery, are in a position to reduce or at least notsignificantly increase the unwanted fluctuations in the voltage at apredetermined point in the network in comparison with the situationwithout a wind power installation or installations.

The invention attains that object, in a method of the kind set forth inthe opening part of this specification, in that the phase angle φ of theelectrical power produced by the wind power installation orinstallations is varied in dependence on at least one voltage detectedin the network.

In a wind power installation of the kind set forth in the opening partof this specification, that object is attained by an apparatus which iscapable of carrying out the method according to the invention.

In a wind park of the kind set forth in the opening part of thisspecification, that object is attained by at least one respectiveapparatus which is suitable for carrying out the method according to theinvention, and a respective voltage detection device, for eachseparately regulatable part of the wind park.

The invention avoids unwanted fluctuations in the voltage applied at theconsumer, in particular the electrical voltage prevailing in a network,by the phase angle of the delivered power being varied in dependence onthe voltage of the consumer or the network. That compensates forunwanted fluctuations in voltage, which arise out of changes in theactive power delivered by the wind power installation or installationsand/or the power taken from the network by the consumers.

In a particularly preferred feature the phase angle is altered in such away that the voltage at least one predetermined point in the networkremains substantially constant. In that situation, to obtain therequired regulating parameter, the voltage at least one point in thenetwork is detected.

In particular that point can be a point other than the feed-in point.That detection of the magnitude of the voltage and a suitable change inthe phase angle of the electrical power delivered by the wind powerinstallation or installations can provide a quickly reacting andeffective regulating system.

In a particularly preferred embodiment the values to be set for thephase angle are derived from predetermined characteristic values. Thosecharacteristic values can preferably be provided in the form of a tablein which a previously determined family of characteristic curves isrepresented in the form of discrete values, this making it possible todeduce the phase angle to be set.

In a preferred development of the invention the regulation system candirectly or indirectly provide that, if the voltage fluctuations haveexceeded the predetermined limit values, the voltage is brought backinto the tolerance range again by the actuation of a switching device inthe network, for example, a step transformer. At the same time or inrelation thereto the phase angle is set for a predetermined period oftime to a constant value—preferably a mean value, for example, zero, inorder once again to be able to compensate for subsequently occurringvoltage fluctuations, by a suitable change in the phase angle.

In a particularly preferred development of the invention suitablevoltage detection procedures and setting operations in respect of thephase angle can also be implemented separately in electrically separateportions of the network, in order to regulate each portion in such a waythat the voltage in each of the portions remains substantially constant.

A further development of the wind power installation according to theinvention advantageously provides a regulating device having amicroprocessor, as in that way it is possible to implement digitalregulation.

A preferred development of the wind park set forth in the opening partof this specification provides that there are a respective apparatuswhich is suitable for carrying out the method according to the inventionand a respective voltage detection device for each separatelyregulatable part of the wind park so that electrically separate portionsof the network can also be separately regulated in such a way that thevoltage in each portion of the network remains substantially constant.

The invention is described hereinafter by means of an embodiment of amethod of operating a wind power installation, with reference to thedrawings in which:

A wind power installation 2 diagrammatically shown in FIG. 9, having arotor 1, is connected to an electrical network 6 which, for example, canbe a public power network. A plurality of electrical consumers 8 areconnected to the network. The electrical generator 12 shown in FIGS. 1and 10 of the wind power installation 2 is coupled to an electricalcontrol and regulating apparatus 10 which firstly rectifies thealternating current produced in the generator and then converts it intoan alternating current at a frequency which corresponds to the networkfrequency. The control and regulating apparatus 10 has a regulatingdevice according to the invention.

A voltage detection device 22 can be provided at any point 22 in thenetwork 6, the voltage detection device measuring, besides the phase inparticular the magnitude of the network voltage and returning themeasured value to the regulating device 10 as a suitable regulatingparameter.

FIG. 10 illustrates the regulating device according to the invention.The diagrammatically illustrated rotor blades 1 are coupled to agenerator 12 which produces electrical power which can depend on thewind speed. The ac voltage produced in the generator 12 can firstly berectified regulator 10 and then converted into an ac voltage of afrequency corresponding to the network frequency.

The network voltage is measured at a location 22 in the network 6 bymeans of a voltage detector (not shown). In dependence on theascertained network voltage—possibly by means of a microprocessor shownin FIG. 4—an optimum phase angle φ is calculated. The network voltage Vis then regulated to the desired value V_(ref) by means of theregulating device.

The electrical power delivered by the generator 12 to the network 6 isregulated by the change in the phase angle.

The view shown in FIG. 12 illustrates the relationship between thevoltage in the network and the phase angle. If the voltage deviates fromits reference value V_(ref) which is between the voltage values V_(min)and V_(max) then, corresponding to the characteristic curve in thegraph, the phase angle φ is altered in such a way that, depending on thesign of the deviation, either inductive or capacitive reactive power isfed into the network in order in that way to stabilize the voltage atthe voltage detection point (at 22 in FIG. 9).

FIG. 11 shows some of the main components of the control and regulatingapparatus 10 illustrated in FIG. 9. The control and regulating apparatus10 has a rectifier 16 in which the alternating current produced in thegenerator is rectified. A frequency converter 18 connected to therectifier 16 converts the initially rectified direct current into analternating current which is fed into the network 6 in the form of athree-phase alternating current by way of the lines L1, L2 and L3.

The frequency converter 18 is controlled by means of a microprocessor 20which is part of the overall regulating device. For that purpose themicroprocessor 20 is coupled to the frequency converter 18. The inputparameters for the microprocessor 20 are the currently prevailingnetwork voltage V, the electrical power P of the generator, thereference value of the network voltage V_(ref) and the power gradientdP/dt. The change according to the invention in the power which is to befed in is implemented in the microprocessor 20.

FIG. 13 shows two wind power installations 2 a and 2 b, as an example ofa wind park. A regulating apparatus 10 is associated with each of thosewind power installations 2 which naturally can also symbolically standfor a respective plurality of wind power installations. The regulatingapparatus 10 detects the voltage at predetermined points 22, 27 in thenetwork 6, 17 and transmits the voltage by way of lines 25, 26 to therespectively associated regulating apparatus 10.

The portions 6, 17 of the network can be connected together or separatedfrom each other, by way of a switching device 23. Provided in parallelwith the switching device 23 is a switching device 24 which makes itpossible for the two regulating apparatuses 10 to be connected togetheror separated from each other, according to the switching condition ofthe switching device 23.

If therefore the two portions 6, 17 of the network are connectedtogether, then the two regulating apparatuses 10 are also connected toeach other so that the entire network is considered as a unit and issupplied by the entire wind park as a unit, wherein the wind park isagain regulated in unitary fashion in dependence on the voltage at thedetection point 22, 27.

If the two portions 6, 17 are separated by the switching device 23, theregulating apparatuses 10 are also separated from each other in such away that a part of the wind park is monitored by a detection point 22 byway of a line 25 by the regulating apparatus 10 and the associated partof the wind park can be correspondingly regulated, while the otherportion of the network 17 is monitored by a detection point 27 by way ofa line 26 by means of the regulating apparatus 10 which correspondinglyregulates the other part of the wind park to stabilize the voltage inthe portion 17 of the network.

It will be appreciated that this division does not have to be limited totwo portions. It can be 3, 4 or 5 portions. That division can be takenas far as associating an individual installation with a portion of thenetwork.

Central regulation of a wind park, in accordance with the invention,generally aims to provide that the wind park not only feeds electricalenergy into a public power supply network but also at the same time canbe controlled in such a way as to support the network, preferably by theoperator of the public network power supply utility. Insofar asreference is made to a wind park in the present application, that isalso intended to denote an individual wind power installation and notonly always a plurality of wind power installations, in which respect itis preferably precisely a plurality of wind power installations thatalways forms a wind park.

For the central control of the wind park, in accordance with theinvention, the operator of the public power supply network not only hasa control access by means of a suitable control line (bus system) to thewind park/to the wind power installation, but he also receives from thewind park/wind power installation data, such as, for example, measuredwind data, data about the status of the wind park, and also, forexample, data about the available power (currently prevailing power)(active power)) of the wind park.

Such a central control can also mean, for example, that the wind park isentirely taken off the network in certain circumstances, for example, ifthe network connection rules which are preset by the operator of thepublic supply network cannot be observed on the part of the wind park.

If, for example, the voltage in the network falls below a givenpredetermined value, for example, to a value of between 70 and 90% ofthe network voltage, the wind park must be separated from the networkwithin a predetermined time, for example, between two and six seconds.

Finally it is necessary to provide that the change in power (dP) of thewind park is not only predetermined by the wind but can also still alterat entire given time intervals. That power parameter is therefore alsoreferred to as the power gradient and specifies by how many percent therespective available power may alter within a predetermined time (forexample, per minute). Thus, for example, it can be provided that thepower gradient of the wind park may be at a maximum between 5 and 15%,preferably 10% of the network connection capacity per minute.

Such regulation of the wind park can be effected, for example, by allwind power installations of a park simultaneously or uniformlyincreasing their power delivery in the predetermined power gradient. Itwill be appreciated that alternatively it is also possible to envisagethat, in the case of a wind park of, for example, between 10 and 20installations, firstly one or two installations (at the respective orderof magnitude of the power gradient) initially feed into the network atfull power and then in accordance with the respective predeterminedpower gradient further installations are cut in, within a predeterminedtime, until all of the available power of the wind park can be fed intothe network.

A further aspect of the wind park regulation according to the inventionis the provision of the reserve power at the level of a percentage, forexample, 10%, of the currently available power of the wind park, or afixed value, for example, between 500 kW and 1 MW or more per wind park.That reserve power is not to be confused with a park power which exceedsthe network connection power of the wind park. The reserve powerdecisively involves a power reserve (this concerns both active power andalso reactive power) which it does not exceed in the range of thenetwork connection power. That reserve power can be prescribed by theoperator of the public supply network. That is to say, if thereforesufficient wind is available to feed the network connection power fromthe wind park into the network, the power supply utility, by virtue ofthe prescribed control intervention into the wind park, can provide thatthis theoretically possible power is not completely fed into thenetwork, but a part of that power remains available as reserve power. Aparticular aspect of that reserve power is that, in the event of anunexpected failure of power station power (at other locations at whichpower is fed into the network), the network can be stabilized by way ofcalling up the corresponding reserve power.

Accordingly, with the above-indicated central control of the wind park,the power fed into the network is under normal circumstances thereforeless than the power to be made available by the wind park (maximumavailable power), in dependence on the respective power requirement inthe network.

So that this above-described power control procedure can be implemented,the network operator also requires the prescribed data such as windspeed, installation status of the wind park (how many installations arein operation, how many are out of operation or damaged) and preferablyalso the maximum possible active power delivery. In that respect, inregard to the maximum possible active power delivery, the limitation canapply that this has to be provided in the form of data only when itcannot be determined from the wind speed and the installation status.

A normal bus system, for example, also a standardized bus system, can beused for control of the wind park and also for data supply for the powersupply utility. There are already standardized interfaces for suchstandardized bus systems, for example, a Profibus system, so thatcentral wind park control can also be implemented by means of suitablystandardized control commands.

Supplemental to the foregoing, it can also be provided that the windpark, as from a pre-designed power, that is to say at a total poweroutput of more than 50 MW, is treated as a large-scale power station andthen must also satisfy the conditions for large-scale power stations.

Finally it can also be provided that the wind park is so regulated thatthe network connection value (the network connection capacity) is notexceeded.

Finally when switching on/cutting in the wind park it is also necessaryto provide that unwanted network retroactions do not occur. For example,when switching on/cutting in a wind park, the current may not be higherthan a predetermined value in respect of the nominal current whichcorresponds to the connection capacity. Such a value can be, forexample, in the range of between 1.0 and 1.4.

If the frequency in the public power supply network rises then—asalready described—it should be provided that, from a given frequencyvalue, for example, from 50.25 Hz (with a nominal frequency of 50 Hz),the delivered active power of the wind park is automatically reduceduntil the network frequency is again stabilized at a value as describedabove.

Therefore it must also always be possible to operate the wind park at areduced level of power delivery in order to be able to observe thenetwork requirements. That power regulation also means that the powerdelivery (in particular active power) can be reduced to any desiredvalue in any operating condition and from any operating point.

Thus, for example, it is possible to implement limitation of the feed-inpower below the available feed-in power if there are dangers in regardto safe reliable system operation, bottlenecks or a risk of overloadingin upstream-disposed networks are to be fixed, there is the danger ofthe formation of an island network, static or dynamic stabilities areendangered, the frequency rise can endanger the entire network system,and for example, repair operations or other operational-governedstoppages also have to take place at the power supply utility.

Besides the active power delivery which has already been described aboveand which is to be afforded if necessary, it must also be possible toprovide a given reactive power, in which case it can also be set aswished by the power supply utility, more specifically both in theinductive and also in the capacitive range, that is to say underexcitedand overexcited, in which respect the respective values can bepredetermined for that purpose by the power supply utility.

In that connection, the reference value in respect of reactive powerprovision can be set variably, wherein the reference value presetting iseffected at the network connection nodes for the power factor (cos phi)or a voltage magnitude. It is also possible to predetermine a fixedreference value.

As already described hereinbefore the power delivery is reduced and/orthe wind park is completely taken off the network if frequency values inthe network exceed/fall below certain levels. Thus, for example, thewind park can be taken off the network when the network falls below anetwork frequency of about 48 Hz (with a 50 Hz network frequency) or at51 to 52 Hz. In that respect, at values below the intended range, it isstill possible to provide within limits of the range that only a part ofthe current available power is fed into the network, for example,between about 80 and 95% of the current available power.

If, for example, the network voltage should also fall below apredetermined value, the same also applies here, as in the case of thedeviating network frequency. In other words, when the voltage fallsbelow or exceeds a predetermined network voltage in the given voltage,firstly a reduced power delivery takes place and, when the networkvoltage falls below or exceeds given limit values, the installations arecompletely taken off the network or at least the power fed into thenetwork is set at zero.

Finally it can also be provided that, when given network voltage and/ornetwork frequency values are reached, tried-and-tested shut-down of thewind park is effected, without a power delivery which has already beenreduced being implemented beforehand.

That however also means at the same time that, with given frequencydeviations/voltage deviations within a predetermined range around thenetwork frequency/network voltage, automatic separation of the wind parkfrom the network is not admissible.

Finally, for network protection purposes, it can also be provided thatthe shut-down time when the voltage value is exceeded is markedlyshorter (for example, between 50 and 200 milliseconds) than in the caseof voltage reduction protection (shut-down time of more than 1 second,preferably between about 2 and 6 seconds). In that respect, theshut-down time when the value of the upper frequency or lower frequencyexceeds or falls below the predetermined, still just admissible limitvalue, is approximately in the region of the shut-down time when thevoltage is in excess (above a predetermined voltage value).

Finally in the event of a fault in the network, for example, in ashort-circuit situation, automatic separation of the wind park from thenetwork should not always occur straightaway, but rather the wind parkcan also be controlled in such a way that, depending on the respectivenetwork connection, it still feeds into the network a contribution tothe short-circuit power as apparent power in order in that way still tobe able to afford network support to a certain degree. This means thatthe wind park, at least for a certain time for the duration of a shortcircuit but at a maximum only a few seconds, has to deliver the highestpossible apparent current (apparent power) which however corresponds,for example, to once or up to 1.5 times the current which corresponds tothe network connection capacity.

The above-described behavior can also be made dependent on the level ofthe nominal voltage, for example, if it exceeds a predetermined valueof, for example, more than 50 kV.

So that the above-described shut-down procedures can take place in goodtime, for example, a protective relay (distance protective relay) is tobe installed for the implementation thereof at the network connectionnode.

Finally means should also be provided which, upon start-up of a windpark, synchronize the voltage in the network and that of the wind parkbecause, when the wind park is started up again, asynchronous voltagessensitively disturb the network and can cause it to shut down.

Insofar as in accordance with the present invention the power isregulated below a value of the power which is to be currently madeavailable by a wind park, that can be implemented by various measures.

Thus, for example, the power can overall be reduced for each individualinstallation so that the entire wind park assumes the desired reducedpower value. As an alternative thereto however it can also be providedthat only individual installations are reduced in respect of their powerfeed-in value so that the total feed-in power value of the wind parkagain assumes the desired value.

Finally it can also be provided that, for example, a given power madeavailable by the wind park is put into intermediate storage in so-calleddump loads (resistors) or other energy storage means or is convertedinto another form of energy, such that the feed-in value of the windpark assumes the desired value.

The reduction in power output can also be afforded by a procedurewhereby one wind power installation or given wind power installationsare entirely removed from the network so that then once again theoverall power of the wind park (in particular the active power thereof)can be set to the desired value and/or drops below the desired value.

For data transmission of the data in respect of the wind park (winddata, status data, power data etc) or for control of the wind park, itis also possible to provide a wireless communication arrangement so thatthe control data or information data can be wirelessly transmitted andprocessed.

In the case of the above-mentioned wind park regulation, it is also tobe provided that, within the wind park, the procedure also involvesascertaining the value which can be made available as maximum energy andalso then further ascertaining what amount of energy is fed into thenetwork so that, taking the difference amount which is substantially dueto control of the wind park on the part of the power supply utility, itis possible to calculate a feed-in recompense amount which if necessaryis reimbursed.

As already described it is not only possible for the power supplyutility which operates the power supply network to have the possibilityof limiting or restricting the power output of the wind park orindividual wind power installations with the access by way of a controlline, for various reasons (network protection, servo power), but it isalso possible for the operator of the public power supply network, atthe same time, to obtain data relating to the status of the wind park,for example, data relating to the maximum available power, wind speedand so forth. As, when the power is restricted to below the currentlyavailable power, the wind park or the wind power installations of a windpark are not put to optimum use, that results in feed-in losses on thepart of the wind power installation operators. Therefore here too theinvention proposes the provision of a virtual current meter whichdetects the difference in respect of that which is not taken off by theintervention on the part of the power supply undertaking into theregulation system and thus the limitation in respect of the wind park orwind power installation power output. Such a ‘virtual current meter’ canon the one hand ascertain from the wind speed the power which is to beavailable and, if at the same time the power supply undertaking oranyone else reduces the power output of individual wind powerinstallations or an entire wind park below the power output which can bemade available, then by an integration operation it is possible toascertain (count) the amount of energy which is not fed into thenetwork. The virtual current meter makes it possible for the operator ofthe wind power installation to obtain remuneration also for the ‘virtualcurrent’, that is to say the current which is not fed into the networkby virtue of the interventions in regulation of the power supply. The‘virtual current meter’ can be installed both at the operator of thewind power installation, in the wind power installations themselveswithin the wind park, at the power supply undertaking or also at themanufacturer of the wind power installations.

Insofar as the present application uses the term wind powerinstallation, that is synonymous with the term wind park. Insofar as thepresent application describes various aspects of the invention they canbe embodied together with the wind power installations or the controlthereof. It is however also possible for the different approachesaccording to the invention to be implemented and claimed singularlywithout the further aspects of the invention, even if the presentapplication usually describes various aspects of the invention together.It will be clear to the man skilled in the art however that variousaspects of the invention can also be implemented and claimed differentlyand the common description thereof is thus not equivalent to them alwayshaving to be implemented and claimed together.

1. A wind park, comprising: at least one wind power installation havinga generator to deliver electrical power to an electrical network, thewind power installation being adapted to vary the amount of theelectrical power that is delivered to the electrical network independence on a network frequency of the electrical network; a frequencysensor circuit coupled to receive the frequency of the electricalnetwork; a control circuit coupled to the wind power installation andreceiving an input from the frequency sensor circuit, the controlcircuit being configured such that the electrical power which isdelivered by the wind park and fed into the electrical network isreduced when the network frequency of the electrical network deviatesfrom a defined value by a threshold amount.
 2. The wind park accordingto claim 1 wherein the electrical power which is delivered by the windpark and fed into the electrical network is reduced when the networkfrequency of the electrical network exceeds or falls below a definedvalue.
 3. The wind park according to claim 1 wherein the thresholdamount is in the range of 0.3% to 0.6% of the network frequency.
 4. Thewind park according to claim 1 wherein the at least one wind powerinstallation comprises: a rotor and an electrical generator coupled tothe rotor to deliver electrical power to the electrical network, and aregulating device with a frequency detector to measure a frequency ofthe electrical power applied to the electrical network and theelectrical power delivered to the electrical network by the wind park isadjustable in dependence on the network frequency measured by thefrequency sensor circuit or can be adjusted from an exterior.
 5. Thewind park according to claim 4 wherein the regulating device includes amicroprocessor.
 6. The wind park according to claim 5 wherein the windpower installation includes an inverter coupled to the microprocessor.7. The wind park according to claim 1 wherein mechanical power of thewind power installation is produced by adjustable rotor blades being setinto wind.
 8. The wind park according to claim 1 wherein the definedvalue is 50 Hz.
 9. The wind park according to claim 1 wherein thedefined value is 60 Hz.
 10. The wind park of claim 1 wherein theelectrical power fed into the electrical network is reduced when thenetwork frequency of the electrical network is greater than the definedvalue by the threshold amount.
 11. The wind park of claim 1 wherein theelectrical power fed into the electrical network is reduced when thenetwork frequency of the electrical network is less than the definedvalue by the threshold amount.
 12. A wind park, comprising: at least onewind power installation having a generator to deliver electrical powerto an electrical network, the wind power installation being adapted tovary the amount of the electrical power that is delivered to theelectrical network in dependence on a network frequency of theelectrical network, a frequency sensor coupled to the electrical networkfor measuring the frequency of the electrical network; a control circuitcoupled to the output of the wind power installation and to thefrequency sensor, the control circuit being configured to reduce thepower output from the wind power installation onto the electricalnetwork when the measured frequency of the electrical network variesfrom a defined value by more than a threshold amount.
 13. The wind partaccording to claim 12 further including: a rectifier circuit coupled tothe output of the at least wind power installation for converting the ACvoltage output of the wind power installation to DC voltage; and avoltage inverter circuit coupled to the output of the rectifier circuitfor converting the DC voltage to an AC voltage having the frequency andvoltage level of the electrical network.
 14. A wind park, comprising: awind turbine means for generating electricity, the wind turbine meanshaving a plurality of blades that rotate based on power from the windand an electrical generator means for generating power from the rotatingblades; power transfer means for transferring the generated power fromthe wind turbine means to an electrical network that is outside of thewind turbine means; a frequency sensor means for receiving the frequencyof the electrical network; a control means for reducing the amount ofpower transferred from the wind turbine means to the electrical networkwhen the network frequency of the electrical network deviates from adefined value by greater than a threshold amount.
 15. The wind parkaccording to claim 14 wherein the threshold amount is in the range of0.3% to 0.6% of the network frequency.